Speed governing systems for steam turbines



May 16, 1967 w. G. WATSON SPEED GOVERNING SYSTEMS FOR STEAM TURBINES 2Sheets-Sheet 1 Filed June 4, 1.965

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INVENTOR WILLIAM GEORGE WATSON BY of w 0 1 ATTORNEYS May 16, 1967 w. s.WATSON 3,319,422

SPEED GOVERNING SYSTEMS FOR STEAM TURBINES Filed June 4, 1965 2Sheets-Sheet 2 TO RELAY OPERATED GOVERNOR VALVE F/GZ -1'o 'couneussaINVENTOR ATTORNEY -T0 STEAM LINE WILUAM GEORGE MTSON United StatesPatent 3,319,422 SPEED GOVERNING SYSTEMS FOR STEAM TURBINES WilliamGeorge Watson, Whitley Bay, England, assignor to C. A. Parsons &Company, Limited, Newcastle-upon- Tyne, England, a corporation of GreatBritain Filed June 4, 1965, Ser. No. 461,304 Claims priority,application Great Britain, June 5, 1964, 23,494/ 64 9 Claims. (Cl.60105) This invention relates to speed governing systems for steamturbines.

As is well known in the art, it is common practice to control the speedand load of a large steam turbine plant such as that used in largeelectrical power stations by means of governing systems which arebasically hydraulic systems. In such systems a turbine driven governorcontrols the pressure of hydraulic fluid which is used to operate relayswhich in turn control the operation of the governor valves which controlthe supply of steam to the turbine. It is customary or usual toincorporate in such governing systems turbine unloading means operablein response to changes in one or more predetermined operatingconditions. Such unloading means may, for example, incorporate devicessensitive to vacuum in the condenser or to the steam pressure at themain steam stop valve, or both types of device may be included. Anydeparture from predetermined values of vacuum or stop valve pressure isdetected, and the load of the turbine is adjusted to meet the newconditions. The adjustment of the turbine load may be effected byaltering the opening of the governor valves independently of thegovernor. Thus the turbine load is altered independently of anyoperation of the speed governor.

It is often desirable that the turbine be prevented from taking up loadautomatically on restoration of normal conditions in the condenser or atthe stop valve. This automatic reloading of the turbine may take placebecause the adjustment of the turbine load as a result of the operationof the devices sensitive to vacuum or stop valve pressure is effectedindependently of the governor. The governor setting, therefore, remainsat the setting which existed prior to the unloading of the turbine bythe unloaders, and immediately upon the restoration of normal conditionsof vacuum or stop valve pressure, the load on the turbine normally wouldreturn to its original value, the turbine speed then being controlled asbefore by the original setting of the speed governor.

It is an object of this invention to provide a speed governing systemfor a steam turbine which enable the turbine to be brought back to itsoriginal load at the discretion of the operator by adjustment of thegovernor setting following load shedding of the turbine as a result ofthe operation of the turbine unloading means.

More specifically, it is an object of this invention to provide such asystem which provides for automatically adjusting the governor settingto correspond to the reduced load on the turbine when the unloaderdevices operate to reduce the load on the turbine, whereby the turbinewill not automatically return to its loaded condition upon restorationof normal conditions, or when the unloader devices cease to operate orare restored partly or wholly to their original position.

It is a further object to provide such a system which incorporates apressure converter so as to permit the use of different fluids in thehydraulic system.

The invention generally consists in a speed governing system for a steamturbine incorporating a governor operable in response to changes inturbine speed, a hydraulic system the pressure of hydraulic fluid inwhich is varied by changes in governor setting, a governor valve "icecontrolling the flow of steam to the turbine in response to changes inpressure in the hydraulic system, and turbine unloading means operablein response to changes in one or more predetermined operating conditionsto vary the pressure in the hydraulic system independently of anyoperation of the governor so as to reduce the steam flow to the turbine,the unloading means being adapted to automatically adjust the governorsetting to correspond to reductions in turbine load produced byoperation of the unloading means, whereby the turbine will not return toits loaded condition when the unloading means ceases to operate or isrestored to its original setting, except under the control of theoperator of the plant.

The invention further consists in a turbine speed governing systemcomprising a governor valve for controlling the flow of steam to aturbine, a governor hydraulic system for variably controlling thegovernor valve in accordance with the pressure of the governor hydraulicsystem, a governor for varying the pressure of the governor hydraulicsystem in response to changes in turbine speed, an unloader hydraulicsystem, means for varying the pressure in the unloader hydraulic systemin response to changes in at least one predetermined operating conditionof the turbine other than speed, and differential pressure meansoperable in response to a predetermined differential pressure betweenthe governor hydraulic system and the unloader hydraulic system toadjust the governor setting so as to vary the pressure in the governorhydraulic system in the sense to reduce the opening of the governorvalve, whereby when the pressure in the unloader hydraulic system isvaried in response to changes in the predetermined condition to theextent that the predetermined pressure differential is reached, theturbine will be at least partially unloaded and the governor settingwill be adjusted in accordance with the unloaded condition to remain inthe adjusted setting should the pressure in the unloader hydraulicsystem return to its original level.

It is yet a further object of this invention to provide a system of thetype originally described above wherein the hydraulic system comprisestwo separate circuits, a first circuit using a fire resistant fluid andincorporating the governor valve and the unloader means, and a secondcircuit incorporating the governor, a pressure converter connected witheach circuit whereby changes in pressure in the second circuit producedby the governor effect changes of pressure in the fluid in the firstcircuit to operate the governor valve therein, electrical contactsassociated with the pressure converter for closing when the pressure inthe part of the second circuit in the converter 1 exceeds the pressurein the part of the first circuit in the converter by'a predeterminedamount, and a motor connected to the governor and operable on closure ofthe electrical contacts to adjust the governor setting until thepressure difference in the converter between the first and secondcircuits is resorted to its original value, at which time the governorsetting will not be adjusted further but rather will remain in itsadjusted setting.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its operation, togetherwith additional objects and advantages thereof, will best be understoodfrom the following description when considered in connection with theaccompanying drawings, wherein:

FIGURE 1 shows somewhat schematically part of a speed governing systemin accordance with one form of the present invention; and

FIGURE 2 shows somewhat schematically a part of a speed governing systemin accordance with an alternative form of the invention using afire-resistant fluid circuit.

In the speed governing system for a steam turbine as illustrated inFIGURE 1, the system comprises a speed governor 1 of a well known typemounted on shaft 2 which is driven directly or indirectly by theturbine. In a hydraulic system operable by the governor, pilot oil isfed through a pre-set regulating valve i from inlet line c and then tothe governor through ports 3, the oil also being fed through line b torelays operating the governor valves (not shown), which valves controlthe amount of steam admitted to the turbine. If the turbine speedchanges, the position of the plunger 4 in sleeve 5 changes to alter thepilot oil pressure. Thus in the governor shown, an increase in turbinespeed would move plunger 4 to the left of the drawing to uncover a partor the whole of ports 5a in the sleeve 5, thus connecting the pilot oilsystem to drain through line a and reducing the pressure in the system.Reduction of the pilot oil pressure operates the valve relays so as toreduce the opening of the governor valves and hence reduce the steamadmitted to the turbine. Conversely if the turbine speed falls theplunger 4 moves to the right of the drawing to reduce the opening ofports 5a and increase the pilot oil pressure in the system. Thisoperates the valve relays to open further the governor valves toincrease the steam admitted to the turbine. The pilot oil pressure canalso be changed by moving the sleeve 5 for setting purposes under normaloperating conditions.

Incorporated in the governing system is a turbine unloading arrangementwhich in the form shown incorporates a vacuum unloading device 6 and amain steam stop valve pressure unloading device 7. In the formillustrated the vacuum unloading device comprises a casing housing abellows 8 closed at its lower end by a baseplate 9a forming a bellowspiston. The baseplate is formed integral with a hollow plunger 9 whichhas ports 10 formed therein and moves in a ported bush 11. The bush 11is surrounded by a chamber 12 to which pilot oil is admitted. Thebellows 8 is subjected to condenser pressure internally throughconnection 11, the bellows being subjected to atmospheric pressureexternally. Under conditions of normal condenser vacuum the differenceof pressure across the bellows piston holds it against a top stop (notshown), and the ports 10 in the plunger 9 have no communication with theports in the bush 11.

If the condenser vacuum falls the pressure inside the bellows 8increases and moves the plunger 9 downwardly assisted by the action ofspring 13, and at a predetermined pressure in the condenser the plungerports 10 are put into communication with the ports in bush 11. Pilot oilcan then flow from chamber 12 to drain through the ports 10 and 11 andconnection d, thus reducing the pilot oil pressure in the unloadersection of the hydraulic system, and in turn reducing the opening of thegovernor valve to reduce the steam admitted to the turbine in a mannersubsequently to be described.

The stop valve unloading device 7 comprises a casing housing a plunger14 operated through lever 15 by the rod 16 of a spring loaded bellowspiston 17. The chamber 18 containing the bellows piston is connected tothe steam circuit adjacent the main stop valve through connection f,valves k and l, strainer m and inlet 19. The pressure of the steam isreduced before it reaches the device 7 by being tapped from theconnection 1 between orifice 20 and orifice n. The plunger 14 operatesin a ported bush 21 which is surrounded by chamber 22 into which pilotoil is admitted.

Under normal conditions the pressure acting on the bellows piston 17holds the rod 16 against a stop (not shown). The plunger 14 is then inits lowermost position and completely covers the ports in the bush 21,thus preventing escape of oil in the pilot oil system to drain throughconnection e. If the stop valve pressure falls by a predetermined amountbelow normal, the pressure acting on bellows piston 17 is reduced, andthe rod 16 begins to move downwardly under the action of the springloaded bellows piston 17. The lever 15 raises plunger 14 to uncover theports in the bush 21 and allow pilot oil to fiow to drain throughconnection e, thus reducing the pilot oil pressure in the unloadersection of the hydraulic system, and in turn reducing the opening of thegovernor valve thus reducing the steam admitted to the turbine, in amanner to be described subsequently.

Either of the devices 6 and 7 can unload the turb ne completely if thepressures to which they are sensit ve change by a sufficient degree fromtheir normal operating values. In many instances, however, it is notdesirable to unload the turbine completely, and toward this end thedevice 6 may incorporate a spring loaded piston 23 and plunger 24, theplunger 24 operating in a ported bush 25. During normal operatingconditions the pilot oil pressure holds the iston 23 against a top stop,and the ports in the bush 25 allow free access of oil to the chamber 12in device 6 and chamber 22 in device 7. Should either device 6 or 7operate and reduce the pilot oil pressure to a predetermined value, forinstance a value equivalent to 10% load on the turbine, the piston 23and plunger 24 move down to cover the ports in the bush 25 to preventfurther escape to drain, and thus the pilot oil pressure is maintainedat a predetermined minimum pressure.

The unloader hydraulic system, that is, the pilot oil system or circuitoperated by the devices 6 and 7, incorporates a separate pilot oilregulating valve j, and is normally isolated from the governor hydraulicsystem, that is, the pilot oil system or circuit operated by the speedgovernor 1, by means of a non-return valve 29 which forms part of theturbine unloading arrangement. The valve 29 normally remains closed andmaintains the governor hydraulic system isolated from the unloaderhydraulic system, although the valve may open under certain conditionsto permit fiow from the governor hydraulic system to the unloaderhydraulic system as will be described subsequently. To enable thegovernor setting to be adjusted to a new operating load on the turbine,resulting from the operation of devices 6 and 7, the pilot oil system ofthe governor 1 and that of the devices 6 and 7 are connected to adifferential pressure gauge 26 which incorporates electrical contacts 27and forms part of the turbine unloading arrangement. Reduction of pilotoil pressure in the pilot oil system of the devices 6 and 7 to a valueequal to that of the governor pilot oil system as a result of the actionof device 6 or device 7 closes 27 and operates through electricalconnections g a governor motor which adjusts the setting of the governoraccordingly, for example, by adjusting the position of sleeve 5. Uponadjustment of the governor setting the governor pilot oil pressure thenfalls in step with the pilot oil pressure operated by device 6 or device7, and the load on the machine is reduced. If the pilot oil pressure inthe system associated with devices 6 and 7 ceases to fall, the contacts27 will remain open and the governor motor will come to rest with thegovernor remaining at the adjusted setting. On restoration of vacuum orstop valve pressure the device 6 or 7 will return to its normal positionand restore the pilot oil pressure associated with it, but the contacts27 will remain open so that the governor setting remains at a settingcorresponding to the reduced load, the governor oil pressure beingprevented from rising by the non-return valve 29. The load on themachine can then be restored in the normal manner by alteration of thegovernor setting under the control of the operator.

The non-return valve 2 makes provision for the un likely condition thatin certain circumstances the governor pilot oil pressure may not fall asrapidly as that of the devices 6 or 7. Depending upon the possibility ofthis happening, the valve 29 may be arranged to open when the pressurein the pilot oil system of the devices 6 and 7 falls below that in thegovernor pilot oil system so as to equalize the pressure in both systemsthrough pipe 28. Normally, however, when the pressure in the unloaderhydraulic system falls to or substantially to the level of the pressurein the governor hydraulic system the governor setting is adjusted so asto reduce the hydraulic pressure therein before any substantial flowcould take place through valve 29.

Referring now to FIGURE 2, the system illustrated therein comprises amain governor 31 associated with turbine-driven shaft 32. An auxiliarygovernor 31a is also shown, but this is not essential to the invention.Pilot oil is fed via connection 1 and pilot oil regulating valve w tothe governor through :ports 33 and also passes to a pressure converter34. The governor is connected to drain through line 0. The fluid for thegovernor valve relays and for the turbine unloading means is afire-resistant flui-d and is kept separate from the pilot oil system.The fluid system includes pumps (not shown) driven independently of theturbine, and pilot fluid passes through line 1.! and a preset regulatingvalve x to the pressure converter 34 before passing to a relay operatingthe governor valve. In parallel with the converter in the pilot fluidsystem are vacuum unloading device 35 and stop valve pressure unloadingdevice 35a, which are part of the turbine unloading arrangement. Theseare constructed as described in connection with FIGURE 1. Connections q,r, y and z correspond to connections d, e, h and f of FIGURE 1. Thepilot fluid passing to the converter is taken from the pilot fluidsystem of the devices 35 and 35a. Normally the pressure in this systemis constant as the ports of these devices are closed.

The pressure converter comprises a casing in which are located twobellows 36 and 37 mounted back to back with a common floating baseplate38. Connected to baseplate 38 is a plunger 39. Pilot oil is admitted tothe inside of bellows 36, and pilot fluid passing from the converter tothe governor valve relays is admitted to the inside of bellows 37. Theplunger 39 moves in a ported bush E0, arid when the pressure in thebellows 36 equals the pressure in bellows 37 the plunger is in a neutralposition in which the ports in bush 40 are closed, and no flow of pilotfluid takes place through the converter. If the pilot oil pressureincreases, the plunger 39 moves downwardly to allow pilot fluid to flowthrough the ported bush 40 and thence through chamber 41 into the pilotfluid system through line v feeding the governor valve relays. Thisincreases the pressure in the pilot fluid system, thus increasing theopening of the governor valve until equilibrium is again reached in theconverter with the plunger in the neutral position. If the pilot oilpressure falls, the plunger moves upwardly in the ported bush 44 toallow the pilot fluid to flow to drain through line s, thus reducing thepressure in the pilot fluid system at the relays, and consequentlyreducing the opening of the governor valve. To reduce the response timeof the converter to a rapid fall in pilot oil pressure a second pair ofbellows 42 and 43 may be included in back to back relationship as shown.They have a common baseplate 44 to which is attached plunger 45. A fallin the pilot oil pressure moves the plunger 45 upwardly to provide afurther connection between the pilot fluid system at the governor valverelays and the drain.

If the turbine is running at, for instance, full load, and the vacuumunloading device 35 or the stop valve pressure unloading device 35aoperates to lower the pilot fluid pressure supplied to the converter,the pressure after the converter at the valve relays also falls byvirtue of the bypass incorporating non-return valve 29a, and as it fallsbelow the pilot oil pressure the plunger 39 moves downwardly, and theturbine unloading means overrides the governor. The pressures before andafter the converter become equal, and as they fall instep the load onthe turbine is reduced. The pilot oil pressure remains constant duringthe initial stage of the fall in pilot fluid pressure since the governorsetting is not altered.

When a predetermined fall in pilot fluid pressure has taken place, theplunger 39 has moved by a distance sufficient to close electricalcontacts of an electrical switch device 46, which in turn operates thegovernor motor to adjust the governor setting. The governor setting isthen adjusted to correspond with the new load on the turbine asdetermined by devices 35 or 35a. The pilot oil pressure will then beapproximately equal to the pilot fluid pressure. If the pressure in thepilot fluid system associated with devices 35 and 35a ceases to fall theelectrical contacts of switch device 46 open and the governor motorcomes to rest. When the devices 35 and 35a return to normal theelectrical circuit remains open, and the governor will remain at the lowload setting and override the turbine unloading means. The load on theturbine will therefore remain at its reduced value until the governorsetting is adjusted by the operator.

From the foregoing description of the structure and operation of the twoexemplary embodiments, it will be seen that each embodiment provides anunloader arrangement operable in response to changes in at least onepredetermined operating condition of the turbine other than speed tovary the pressure in the hydraulic system in the sense to at leastpartially unload the turbine by partially closing the governor valve,the unloader arrangement providing for automatically adjusting thegovernor setting to correspond to the reduction in turbine load so as toprevent restoration of turbine load when thepredetermined operatingcondition returns to its normal value.

Although I have shown and described certain specific embodiments of myinvention, I am fully aware that many modifications thereof arepossible, and my invention, therefore, is not to be restricted to theprecise details of construction shown and described, but is intended tocover all modifications coming within the scope of the appended claims.

Having thus fully described my invention in the manner required by thepatent statutes, I claim:

1. A speed governing system for a steam turbine, comprising a governorvalve for controlling the flow of steam to a turbine; a hydrauliccontrol system for variably controlling said governor valve inaccordance with the pressure in said hydraulic system; a governor forvarying the pressure of said hydraulic control system in response tochanges in turbine speed so as in turn to control said governor valve;turbine unloading means operable in response to changes in at least onepredetermined operating condition of the turbine other than speed tovary the pressure in said hydraulic system in the sense to at leastpartially close said governor valve, said unloading means includingmeans for automatically adjusting the governor setting to correspond toreduction in turbine load produced by operation of said unloading meansand for leaving the governor setting at its adjusted value upon removalof said predetermined operating condition so as not to restore the loadon the turbine when the unloading means ceases to operate.

2. In a steam turbine plant, a turbine speed governing system comprisinga governor valve for controlling the flow of steam to a turbine; ahydraulic system for variably controlling said governor valve inaccordance with the pressure of the hydraulic system; a governor forvarying the pressure of said hydraulic system in response to changes inturbine speed; an unloader means operable in response to changes in atleast one predetermined operating condition of the turbine other thanspeed to vary the pressure in said hydraulic system in the sense to atleast partially unload the turbine by partially closing said governorvalve, said unloader means including means for automatically adjustingthe governor setting to correspond to the reduction in turbine load soas to prevent automatic restoration of turbine load when said unloadermeans ceases to vary said pressure in said sense.

3. Apparatus as set forth in claim 2 wherein said unloader means isadapted to operate in response to changes in condenser vacuum of a steamcondenser associated with the turbine.

4. Apparatus as set forth in claim 2 wherein said unloader means isadapted to operate in response to changes in steam pressure supplied tothe turbine.

5. Apparatus as set forth in claim 2 in which the hydraulic systemcomprises two separate circuits, a first circuit using a fire-resistantfluid and incorporating the said governor valve and the unloader means,and a second circuit incorporating the governor; a pressure converterconnected with each circuit whereby changes in pressure in the secondcircuit produced by the governor effect changes of pressure in the fluidin the first circuit to operate the governor valves therein; electricalcontacts associated with said pressure converter for closing when thepressure in the part of the second circuit in said converter exceeds thepressure in the part of the first circuit in said converter by apredetermined amount, and a motor connected to said governor andoperable on closure of said electrical contacts to adjust the governorsetting until the pressure difference in the converter between the firstand second circuits is restored to its original value.

6. In a steam turbine plant, a turbine speed governing system comprisinga governor valve for controlling the flow of steam to a turbine; agovernor hydraulic system for variably controlling said governor valvein accordance with the pressure of .the governor hydraulic system; agovernor for varying the pressure of said governor hydraulic system inresponse to changes in turbine speed; an unloader hydraulic system;means for varying the pressure in said unloader hydraulic system inresponse to changes in at least one predetermined operating condition ofthe turbine other than speed; and differential pressure means operablein response to a predetermined differential pressure between saidgovernor hydraulic system and said unloader hydraulic system to adjustthe governor setting so as to vary the pressure in said governorhydraulic system in the sense to reduce the opening of said governorvalve until the differential pressure between the two systems is changedfrom said predetermined value, whereby when the pressure in saidunloader hydraulic system is varied in response to changes in saidpredetermined condition to the extent that the predetermined pressuredifferential is reached, the turbine will be at least partially unloadedand the governor setting will be adjusted in accordance with theunloaded condition to remain at the adjusted setting should the pressurein said unloader hydraulic system return to its original level.

7. Apparatus as set forth in claim 6 wherein said governor operates toreduce the pressure in said governor hydraulic system in response toincreases in turbine speed, wherein said means for varying the pressurein said unloader hydraulic system operates to reduce the pressuretherein in response to changes in said predetermined operatingcondition, and wherein said predetermined pressure differential isreached when the pressure in said unloader hydraulic system falls tosubstantially the pressure in said governor hydraulic system.

8. Apparatus as set forth in claim 7 further comprising a non-returnvalve for permitting flow from said governor hydraulic system to saidunloader hydraulic system.

9. Apparatus as set forth in claim 7 wherein said pressure differentialmeans includes a pair of electrical contacts which are closed when thedifferential pressure reaches said predetermined value and which areopen when the pressure differential is above said predetermined value,and a motor controlled by the closing of said contacts for adjusting thegovernor setting in the sense to reduce the governor hydraulic systempressure to reduce the opening of the governor v alve when said contactsare closed.

No references cited.

MARTIN P. SCHWADRON, Primary Examiner.

R. R. BUNEVICH, Assistant Examiner.

1. A SPEED GOVERNING SYSTEM FOR A STEAM TURBINE, COMPRISING A GOVERNOR VALVE FOR CONTROLLING THE FLOW OF STEAM TO A TURBINE; A HYDRAULIC CONTROL SYSTEM FOR VARIABLY CONTROLLING SAID GOVERNOR VALVE IN ACCORDANCE WITH THE PRESSURE IN SAID HYDRAULIC SYSTEM; A GOVERNOR FOR VARYING THE PRESSURE OF SAID HYDRAULIC CONTROL SYSTEM IN RESPONSE TO CHANGES IN TURBINE SPEED SO AS IN TURN TO CONTROL SAID GOVERNOR VALVE; TURBINE UNLOADING MEANS OPERABLE IN RESPONSE TO CHANGES IN AT LEAST ONE PREDETERMINED OPERATING CONDITION OF THE TURBINE OTHER THAN SPEED TO VARY THE PRESSURE IN SAID HYDRAULIC SYSTEM IN THE SENSE TO AT LEAST PARTIALLY CLOSE SAID GOVERNOR VALVE, SAID UNLOADING MEANS INCLUDING MEANS FOR AUTOMATICALLY ADJUSTING THE GOVERNOR SETTING TO CORRESPOND TO REDUCTION IN TURBINE LOAD PRO- 